Y A M L

Previously YAML was known as Yet Another Markup Language. But now it is called Yaml Ain't Markup Language.

YAML is not a programming language
YAML is a human-readable data serialization language
It is similar to XML & JSON Data type language.
It has a strict syntax and Indentation is important
it can be easily converted into JSON or XML files
The standard format to transfer the data

Key Value Pairs-

Key Value pairs are separated by 'Colon'. The left side of the ' : ' is Key and the right side of the ' : ' is the value. You have to use space after ":" otherwise your content is invalid.

This is key : this is value
1 : this is one

In YAML, you can write 'string' without quotes as well.

comments-

In YAML only you can use a single-line comment by typing '#' .

#this is a comment

Objects-

Here's 'Tourist Places' is 'Object'.

Tourist Places:
            Himachal Pradesh : Shimla
            Chandigarh : Rock Garden
            New Delhi : India Gate

Lists-

The list is represented by ' - '

microservices :
            -app : user-auth #because of '-' this is called a list
            port : 80
            version : 1.7

same as :

list also :
   -one
   -two
   -three

The List under List:

microservices:
            -app : user-auth #this is a list
            port : 80
            version : [ 1.7, 1.9, 2.0 ]  #this is also list but under list

Booleans-

Booleans in YAML: on/off, True/False, Yes/No

microservices:
            -app : user-auth
            port : 80
            deployed : off #here this is called boolean

Multiline String-

In YAML you cannot write multiple lines without ' | '

multiline string :  | #by the use of '|' you can type multiline string
this is
a multi-
line string.

If you have a single line string that has too many words use '>' to put all content in one line

single-line string : > #by the use of '>' you can type single-line string
 this all 
 content 
 will appears in
 the single 
 line .

Environment Variables-

commands :
   -/bin/sh
   - -ec
   - >-
   mysql -h 127.0.0.1 -u root -p$MYSQL_ROOT_PASSWORD_E
   'SELECT 1'
#env var $MY_SQL_ROOT_PASSWORD

SKDJ

Placeholders-

It is a special string that can be replaced with a value at runtime.

database :
   name : ${{ database_name }}

When this file is processed, the value of the 'database_name' env. var. will be substituted for the placeholders. This allows you to use env. var. to config your YAML file.

Multiple YAML documents-

This means you can store two files in one file separated by '---'

apiVersion : v1  
kind : configMap 
metadata :         
        name : Mosquito-config-file
data :
  mosquitoconf : |
   log_dost stdout
   log_type shell
   listener 9001
---
apiVersion : v2
kind : secret
metadata :
        name : Mosquito-secret-file
        type : Opaque      
        data : NULL

A Real World Example :

apiVersion : v1     # key value pairs
kind : configMap 
metadata :          # object
        name : nginx
        labels :    #object
        app : nginx
spec :              #object
  containers :      #list of objects
            - name :nginx-container
            - image : nginx
            - ports :   #list
            - data : NULL